Ultrastructure of the aging myocardium: a morphometric approach.

Left ventricular tissue from adult and aging Syrian hamster heart was compared at the ultrastructural level, using both qualitative and morphometric electron microscopy. The aging myocardium often showed indented nuclei, lipid droplets and aggregations of dense bodies. The volume fractions of muscle cells occupied by mitochondria, lipid and lysosomes (including both primary lysosomes and residual bodies) was significantly greater in the old animals, while there was no significant difference in nuclear volume fraction or myofibrillar mass. Sarcoplasmic reticular volume and membrane surface area fell during aging. The area of mitochondrial inner membrane plus cristae per mitochondrial volume also fell. When sarcoplasmic reticular and mitochondrial area were expressed per myofibrillar volume fraction, the sarcoplasmic reticular ratio fell, while the mitochondrial parameter remained constant. Discoordinate aging of cellular components in the mammalian myocardium is proposed.